Cloning and expression of a tau class glutathione S-transferase (ZjGSTU1) from Chinese jujube in response to phytoplasma infection

Phytoplasmas are associated with diseases of several hundred plant species. Jujube witches' broom disease (JWB) is a destructive phytoplasma disease in Chinese jujube (Ziziphus jujuba Mill.). Ziziphus jujuba Mill. 'J5', an excellent strain with extremely high resistance to JWB, was selected by us. In our previous study, a GST (EC 2.5.1.18) fragment was sequenced from suppression subtractive hybridization library of 'J5' under JWB phytoplasma stress. Based on this result, a GST gene (ZjGSTU1, HM345954) was first isolated from jujube by homology cloning and RACE. ZjGSTU1 contains a complete open reading frame of 702 bp encoding a protein of 233 amino acid residues. Sequence alignment showed that ZjGSTU1 shared a typical conserved structure and high identity with tau GSTs from other plant species. Relative RT-PCR demonstrated that the expression of ZjGSTU1 mRNA in jujube leaves and branches could be triggered by JWB phytoplasma. Moreover, the expression of ZjGSTU1 mRNA in resistant strain 'J5' increased sooner and higher than that in sensitive strain 'J9' under JWB phytoplasma stress ('J5' and 'J9' are two strains from the same cultivar). Western blotting analyses showed that the expressions of ZjGSTU1 in 'J5' and 'J9' were dramatically up-regulated under JWB phytoplasma stress and its expression in 'J5' was also higher than that in 'J9' at protein level. Collectively, this paper highlights that ZjGSTU1 gene is responsive to phytoplasma infection. The possible roles of this gene were discussed in terms of regulatory process in resistance to phytoplasma infection.